BOARD AGENDA MEMORANDUM
SUBJECT:
Title
Groundwater Conditions and Recharge Operations (Responding to Board Member Request R-19-0005).
End
RECOMMENDATION:
Recommendation
Receive an update on groundwater conditions and planned recharge pond operations including the Dr. Robert Gross recharge ponds on Upper Penitencia Creek.
Body
SUMMARY:
Water supply conditions in Santa Clara County have been favorable since the wet winter of 2016-2017 that marked the end of the recent drought. Storage in Santa Clara Valley Water District (Valley Water) and state reservoirs is at nearly 100% of the 20-year average for April. The increased snowpack in the Sierra and improved conditions in the Delta have allowed for higher allocations of imported water from the Central Valley Project and State Water Project, resulting in ample supply available for water treatment plants and the Valley Water managed recharge program. Groundwater storage has fully recovered to pre-drought conditions, with new historic high groundwater levels in many North County wells.
Since 2018, Valley Water has reduced managed recharge operations in the North County since the Santa Clara Subbasin is essentially full and groundwater pumping continues to be low. Full basin conditions are contributing to high artesian pressures in many areas, which has resulted in reports of flowing artesian wells and operational concerns for some retailers. Valley Water staff is planning to maintain a reduced managed recharge program in the North County for 2019 based on extraordinary groundwater conditions, and would like to provide an update to the Board.
Groundwater Conditions
Increased reliance on groundwater and reduced recharge during the 2012-2016 drought lowered groundwater levels and storage. Estimated groundwater storage was about 232,000 acre-feet (AF) at the end of 2015, in the severe stage (Stage 3) of the Water Shortage Contingency Plan (WSCP). With little water for recharge, Valley Water took the opportunity to perform maintenance work on many ponds while empty. By removing fine sediments that accumulated in the ponds over the years, recharge rates increased by more than 60% in some areas.
In 2016, Valley Water recharge of nearly 150,000 AF helped groundwater levels and storage recover substantially from the drought. Following more typical recharge in 2017 and 2018 (about 108,000 AF per year), groundwater storage fully recovered to pre-drought levels, reaching about 352,000 AF and well above the 300,000 AF normal stage of the WSCP (Stage 1). Groundwater recovery was also assisted by low demands due to the community’s continued efforts to save water, and increased reliance on treated water by water retailers.
Groundwater pumping continues to be lower than average due to overall reductions in demand and retailers relying more on treated water. In the past two years, annual pumping in the northern Santa Clara Subbasin has been less than 70,000 AF, far below the long-term average of 92,000 AF.
Groundwater levels and storage have recovered countywide, but are especially robust in the northern Santa Clara Subbasin. This area is called the Santa Clara Plain, and encompasses the areas of the Santa Clara Subbasin north of the Coyote Valley. Groundwater levels are at historic highs in many monitoring wells in the Santa Clara Plain; 23% of wells have set new record highs in 2019 and another 33% are equal to previous record highs. In addition, 18% of the wells in this area are artesian (another record), meaning the groundwater is under enough pressure that it would rise above the land surface if not capped by the well. Overall, 96% of monitoring wells show March/April 2019 groundwater levels being higher than the long-term average (Attachment 1). These measurements, and Valley Water modeling estimates, suggest that aquifers in the Santa Clara Plain are essentially full.
Very shallow groundwater can seep onto roadways, flood basements and other underground structures, increase inflows to sewers, and increase the need for dewatering. Strong artesian pressures can lead to the discovery of old abandoned wells, some of which begin flowing at the land surface. They can also cause concerns for water retailers, who may experience operational issues at their own wells. Shallow groundwater and artesian pressures often peak after wet years, and it is not uncommon to get more frequent reports of abandoned wells or infrastructure flooding in such years. Valley Water and land use agencies are currently receiving numerous related reports.
Planned Recharge Pond Operations
The purpose of Valley Water’s managed recharge program is to balance groundwater pumping and maintain sustainable conditions in the Santa Clara and Llagas subbasins. Due to a reduced recharge plan, many Santa Clara Subbasin recharge ponds were not filled in 2018 and about 80 percent remain offline. Valley Water is maintaining full recharge in ponds and creeks in the Coyote Valley (the southern part of the Santa Clara Subbasin) and Llagas Subbasin since groundwater is the primary water supply in South County and recharge is needed to balance pumping.
Because of the reduced recharge operations in the North County, and the large number of empty ponds throughout the area, Valley Water has received many inquiries from the public. Many of the streams and recharge ponds are adjacent to public trails where trail users are accustomed to seeing ponds full of water. As these ponds have continued to remain dry, we have received many questions asking why the ponds are not being filled.
Valley Water’s recharge ponds are utility facilities and are operated primarily for water supply purposes, though they can provide incidental recreational opportunities. A few North County ponds that are near trails more heavily used by the community have remained in operation. These include some of the Camden ponds off Los Gatos Creek in Campbell, Coyote Percolation Pond in South San Jose, and the McClellen Ponds in Cupertino.
Penitencia Ponds
One of the recharge systems that has received a lot of attention is a series of ponds in northeast San Jose, just north of Penitencia Creek, referred to as the Upper Penitencia Recharge System (Penitencia Ponds). Penitencia Ponds is the general name given to a network of 18 Valley Water groundwater recharge ponds to the north of Upper Penitencia Creek in San Jose (Attachment 2). These ponds are water supply facilities operated to provide controlled recharge of imported water into the Santa Clara Subbasin. Although the Penitencia Ponds are not recreational facilities, several of the ponds are adjacent to public trails and are enjoyed by the public when they are full.
The Penitencia Ponds are laid out in series, starting with the upstream ponds to the east and traversing west (Attachment 3), as follows:
- Dr. Robert W. Gross Ponds (5 ponds)
- Piedmont Ponds (4 ponds)
- Helmsley Pond
- Upper Capitol Ponds (6 ponds)
- Lower Capitol Ponds (2 ponds)
In addition to Valley Water’s 18 ponds, the City of San Jose (City) and Santa Clara County (County) co-own the City Park Pond located in the Penitencia Creek Park. The City Park Pond is managed by the City. Water for the pond is delivered from Valley Water’s Penitencia Pond system when it is operating, otherwise it is not possible for Valley Water to supply water to the pond. When operating, water is delivered via a pipeline that branches off the Helmsley Pipeline that connects the last of the Piedmont Ponds to Helmsley Pond (Attachment 3). Normally, water is delivered to the City Park Pond to provide additional groundwater recharge with a collateral outcome of recreation, a benefit sought by the City.
To get water into the Penitencia Ponds, imported water, delivered to the county via the South Bay Aqueduct, is released from Station 4, a turnout of the South Bay Aqueduct, into the first pond of the Dr. Robert W. Gross Ponds (Pond 1a). Once this pond fills, water flows through a pipe conveying water to Pond 1c. Once pond 1c is full, water will back up in pond 1a and overflow a spillway into pond 1b. Once full, pond 1b overflows into pond 2 which then overflows into pond 3 and so on, as it makes its way to the last of the Lower Capitol Ponds downstream. If one pond in the series is out of operation, all downstream ponds will soon dry up. Attachment 3 shows that the operation of each of the upstream ponds is a condition to operating any downstream pond.
Earlier this season, a 60-foot long culvert pipe and valve between the first two of the Dr. Robert W. Gross Ponds (Pond 1a and 1c) failed, requiring all water into the ponds to be turned off. This allowed the ponds to dry out so staff could access the bottom of the ponds to make repairs. This also caused the entire Penitencia Pond system to be dry including the City Park Pond. The failed pipe and valve were replaced in early May 2019, allowing water to be released into Dr. Robert W. Gross Ponds beginning on May 14. Over the following week the series of ponds began filling until water reached the City Park Pond. Once the City Park Pond was full, releases to the ponds were reduced to only the upper Dr. Robert W. Gross Ponds 1a, 1b and 1c.
Due to the full groundwater conditions, the Penitencia Ponds are not planned to be fully utilized. Only the first three of Dr. Robert W. Gross Ponds, which are adjacent to the Penitencia Creek Trail, will likely be kept full. Releases to the ponds will occasionally be increased in order to supply water to the City Park Pond but the remainder of the Penitencia pond system downstream will remain empty. A full recharge program is not anticipated until groundwater conditions change and additional recharge is needed.
NEXT STEPS
In response to the many public inquiries that have been received regarding Valley Water’s recharge program, an outreach plan will be developed to help inform the public about our recharge operations and provide answers to common questions about the recharge ponds and why some ponds may be empty.
In addition, staff has already met with several water retailers to assess their flexibility to pump additional groundwater rather than using treated water to help in reducing artesian pressures. Also, since local recharge has been reduced, Valley Water has been able to increase carryover storage and out of county groundwater storage in the Semitropic Water Storage District (Semitropic), which is the groundwater storage bank near Bakersfield that provided essential supply to Valley Water during the drought.
Staff will continue to monitor current groundwater levels, operations plans, retailer pumping, artesian conditions, and recharge rates to determine when to resume normal managed recharge operations in the North County. In the South County, managed recharge continues in order to balance ongoing pumping. Healthy groundwater levels are important to help prepare for future droughts. Because we do not know when droughts will occur, we encourage the community to continue to make water conservation a way of life.
FINANCIAL IMPACT:
No actions associated with this item are anticipated to have a financial impact. Adequate staff time to operate Valley Water’s groundwater recharge system is budgeted in the fiscal year budget.
CEQA:
The annual operation of the raw water and groundwater recharge system does not constitute a project under CEQA because it does not have a potential for resulting in direct or reasonably foreseeable indirect physical change in the environment.
ATTACHMENTS:
Attachment 1: Map
Attachment 2: PowerPoint
Attachment 3: Schematic Diagram
UNCLASSIFIED MANAGER:
Manager
Kurt Arends, (408) 630-2284